This invention relates to electronic taxi meters and in particular to a method and system for reducing the repetition rate of pulses signifying either increments of distance travelled or units of waiting time in such a manner that each pulse in the pulse sequence having the reduced repetition rate signifies a determined fare increment. The system and method is to be applicable both to integral and non-integral reduction ratios.
Electronic taxi meters are known and are disclosed, for example, in application Ser. No. 323,907, filed on January, 1973 the claims of which have been allowed. In such taxi meters a first and second pulse sequence is furnished, the pulses in each sequence signifying, respectively, increments of distance travelled and units of waiting time. In these known taxi meters a selection circuit is furnished which selects the pulse sequence having the higher repetition rate for purpose of advancing the taxi meter by a given fare increment. In order that the selection circuits operate as accurately as possible, high repetition rates for the input pulses are desirable. The higher the repetition rate the more exact the switching of the selection from the distance increment to the unit time pulses and vice versa. In known taxi meters of this type, the relatively high frequency pulses at the output of the selection circuits are then applied to a binary reduction stage or the like so that the output pulses of this binary reduction stage then constitute the tariff pulses, that is the pulses each of which causes the taxi meter to be advanced by a fare increment.
A further requirement for the conventional taxi meters of the type described above is that the two pulse sequences applied to the input of the selection circuit must be of sufficiently low frequency that the selection circuit can process the pulses without distortion. The highest allowable frequency of course depends upon the particular electronic building blocks used. However, in any case, the speed of the taxi must be considered to be able to vary between zero and 140 kilometers per hour. If the input pulse frequency or repetition rate is such that one pulse is generated per 0.1 m distance travelled, then the frequency or repetition rate of the pulses each of which signify distance travelled is variable between 0 and approximately 400 pulses per second. If this frequency is again increased by a factor of 10 which of course is possible, then one pulse would be generated per 0.01 meters of distance travelled. Under this condition the selection circuit would have to be able to process pulses having a frequency between 0 and 4,000 pulses per second. This is not always readily accomplished with electronic building blocks and especially is difficult to accomplish with highly integrated circuit building blocks.
On the other hand it must be considered that the pulses at the output of the selection circuit already constitute a measure of the fare. In other words, each pulse at the output of the selection circuit represents a determined fare increment. Since the fare rate for the time and the distance travelled may differ widely, the reduction in the pulse repetition rate must take place individually for the distance and the time pulses and the reduction must be carried out prior to and not following the selection circuit.
If it is now assumed that after the selection circuit a further repetition rate reduction of 100:1 takes place (as is the case in the taxi meter described in the above-mentioned U.S. application) then the reduction ratios given in the following Table must exist for the corresponding values also listed in this Table: Case I: Distance per Fare Reduction Ratio Increment ______________________________________ Fare rate 1 50 m = 500 pulses 5:1 Fare rate 2 35 m = 350 pulses 3.5:1 Fare rate 3 20 m = 200 pulses 2:1 Case II: Fare rate 1 15 m = 150 pulses 1.5:1 Fare rate 2 12.5 m = 125 pulses 1.25:1 Fare rate 3 10 m = 100 pulses 1:1 ______________________________________
The above Table of course constitutes the reduction ratios as applied to the distance increment pulses. For the unit time pulses and the corresponding fare rates, non-integral reduction ratios may also be required. For the usual type of resettable binary reduction stage, the implementation of such non-integral reduction ratios is particularly difficult. In particular it is impossible to implement such non-integral reduction ratios with sufficient accuracy.